1. Field of the Invention
The present invention relates to a current detection circuit for detecting electric current that flows through a photoreceptor device.
2. Description of the Related Art
In various kinds of electronic apparatuses, light input externally is measured, and signal processing is performed based upon the received light amount thus measured. Examples of such electronic apparatuses include an illuminance sensor, a photoreceptor apparatus employed in an infrared ray remote controller, and so forth. Examples of photoreceptor devices for receiving light which are widely used include a phototransistor, a photodiode, a CCD (Charge Coupled Device), etc.
The phototransistor and the photodiode output electric current according to the light thus received. Accordingly, the photoreceptor apparatus amplifies the current that flows through such a photoreceptor device, or performs signal processing such as voltage conversion.
[Patent Document 1]
Japanese Patent Application Laid Open No. 2005-216984
[Patent Document 2]
Japanese Patent Application Laid Open No. H6-29758
[Patent Document 3]
Japanese Patent Application Laid Open No. 2006-339458
In some cases, the current that flows through a photoreceptor device is amplified using a current mirror circuit, and signal processing is performed based upon the current thus amplified. It should be noted that the concept of “amplification” as used here includes amplification with a mirror ratio of 1 or less, in addition to amplification with a mirror ratio which is greater than 1.
In a case in which a current detection circuit must provide high-speed response operation, there is a need to provided bipolar transistors to a current mirror circuit. However, a current mirror circuit configured using the bipolar transistors has a problem as follows. That is to say, with such an arrangement, when the mirror ratio of the current mirror circuit is switched, the base current of each transistor changes. This leads to poor linearity of the mirror ratio with respect to the input current, and reduces the precision of the mirror ratio (which will also be referred to as “mirror ratio precision” hereafter).
Such a problem can be solved by providing, to the current mirror circuit, a compensation circuit for compensating for the base current. However, such an arrangement has a poor performance in a state in which the power supply voltage is low.